The present invention relates to a digital camera having an AF (automatic focusing) mechanism, and particularly to such a digital camera having a function to switch mechanisms between the AF mechanism and an MF (manual focusing) mechanism.
In a digital SLR (single-lens reflex) camera with an AF mechanism, a part of an object image through a photographing lens unit is lead to an AF module, which evaluates the distance between the object and the camera. An image focusing operation is performed by a CPU, which is built inside the camera, driving a plurality of lenses that configure the photographing lens unit based on the evaluated distance. An example of such technique is disclosed in Japanese Patent Provisional Publication No. P2004-251999, which discloses a digital camera provided with an AF motor to generate rotary drive force. The rotary drive force is conveyed to the photographing lens unit, and drives some of the lenses in a direction of the optical axis to a focused position.
When AF is performed, the lenses are first driven to a relatively close point to the focused position in a coarse and fast movement, then driven in a fine and slow movement from the close point to the focused position. With these movements, focusing on the object is accomplished smoothly in a short time even when the lenses are apart from the focused position.
In an AF mechanism such as above, however, backlashes between various gears and screws configuring the AF mechanism often cause huntings, i.e., the lenses are not settled in the focused position, and focusing is not accomplished.
When the photographing lens unit of the camera with the AF mechanism is manually controlled, the lens drive mechanism needs to be detached from the AF motor. An example of such a switching mechanism to detach the AF motor is disclosed in U.S. Pat. No. 6,788,890, which discloses a switching mechanism operated manually. Such a manual switching operation may be troublesome, specifically when immediate switching from AF to MF is required, as releasing the AF mechanism and focusing manually may take time, and a right moment for photographing may pass.